Interlocked blade shrouding



Feb. 14, 1961 H. w, WELSH INTERLOCKED BLADE SHROUDING 2 Sheets-Sheet 1 Filed Aug. 14, 1957 Feb. 14, 1961 H. w. WELSH INTERLOCKED BLADE SHROUDING 2 Sheets-Sheet 2 Filed Aug. 14, 1957 ATTORNEY United 7 States Patent INTERLOCKED BLADE SHROUDING Harvey W. Welsh, Indianapolis, Ind., assignor to General l1V)Iotors Corporation, Detroit, Mich a corporation of elaware Filed Aug. 14, 1951, Ser. No. 678,090

6 Claims. 01. 253-77 1 be closely spaced at the hub, but are widely spaced at the tip. Since such machines may be of considerable diameter and rotate at high speed, there is a high centrifugal force on the shroud. My invention is directed primarily to the provision of a suitable lightweight shroud structure which will not put a heavy radial'load on the blades and yet which is sufliciently rigid that it will not bow out to a harmful extent between the blades, and to a simple, lightweight, reliable, and readily applied attachment for the shroud which makes it practicable to remove the shroud for replacement of damaged blades.

The blade shrouding structure of the present invention represents a different approach to the problem of shrouding rotor blades from that described in my US. Patent No; 2,963,272. a

The nature of the invention and the advantages thereof will be apparent to those skilled in the art from the succeeding detailed description of the preferred embodiment of the invention and the accompanying drawings thereof. Figure l is a fragmentary sectional view of the rotor of an axial-flow compressor taken on a plane normal to the axis of the rotor.

Figure 2 is a fragmentary exterior view of the rotor with parts cut away and in section.

' Figure 3 is a sectional view taken on the plane indicated by the line 3 3 in Figure 2.

Figure 4 is a view of the blade tip.

Figure 5 is a sectional view through'the shroud taken in the plane indicated by the line 55 in Figure 1.

Figure 6 is an exploded View, with parts cut away, illustrating the connection of the shroud to the blade.

Figure 7 is a partial elevation view of a compressor rotor.

The structure of the rotor is illustrated generally in Fig. 7. The details of the rotor wheel'and blade root are, of course, immaterial to this invention. Fig. 7 shows a rotor wheel or disk 8 in which are engaged the roots 9 of blades 10, to the tips of which is attached a shroud composed of segments 12.

Referring to Figure l, the rotor includes a ring of blades 10 which may be of the usual airfoil contour indicated in Figure 2, or any form suited to the particular compressor. The 'blades extend from the rotor wheel or disk 8. A shroud structure extending around the tips of the blades is defined by a number of shroud segments 12 preferably equal in number to the number of blades, each "segment extending from the tip of one blade to the tip of the next with the ends of the segments'overlapping at the blade and being secured to the blade tip. The shroud segment is principally a sheet metal structure, as most clearly shown by Figure 5. It comprises an inner arcuate strip 13, a hat section strip 14, the marginal flanges of which are brazed or spotwelded to the edges of the strip 13, and a channel section strip 16. The base ofthe channel is preferably spotwelded to the base of the hat section so that the flanges 17 of the channel strip extend outwardly to provide labyrinth seal flanges which closely approach the case of the compressor to minimize leakage across the tips of the blades.

A generally T-shaped block 18 is welded or brazed in the space between the strips 13 and 14 at one end of the segment. The leading and trailing edge portions of the strips are cut away to conform to the shape of the block, .the strips and block defining a tongue 19 extending from. the end of the segment. Two L-shaped blocks 21 and 22 are similarly mounted in the space between the strips 13 and 14 at the other end of the segment. The central part of the webs 'of the strips 13, 14, and 16 is cut out so that this end of the shroud defines two tongues ,23 and 24 which extend on each side of the tongue 19 when the shroud segments are mounted on the blades. The tongue 19 fits closely between the tongues 23 and 24. 7

An undercut or dovetail slot 26 extends spanwise of the blade through the three tongues 19, 23, and 24. The

portions of the slot in the two segments are aligned when the shroud is assembled. The walls of the slots ledges 27 facing outwardly from the rotor. 1

Each blade 10 includes a head portion 28 extending chordwise of the blade, preferably for about three-fifths of the chord of the blade. As will be clearly apparentin Figures 3 and 4, this head is of H-shaped cross-section having slots 29 in the sides of the head. The outer surfaces of the slots provide abutments 31 facing inwardly toward the rotor. The surfaces 32 of the head are adapted to engage the inner radial wall 33 of the slot 26 with a slight clearance so that the shroud segments can readily be dropped over the head of the blade.

As will be apparent from the drawings, the tip of the blade is skewed with respect to the axial direction through .the rotor so that the head 28, slot 26, and, in general, the structures defining the tongues 19, 23, and 24, are similarly skewed.

To assemble the shroud segments on the blades, the overlapping ends of two adjacent segments are dropped over the head of the blade with the tongue 19 extending between the tongues 23 and 24. The shrouds are held in place against centrifugal force, which would tend to move them outwardly, by two keys 34 which are L shaped in cross-section, one flange of the key entering the slot 29 in the blade head and the other flange extending radially outward between the blade head and the radial walls of slot 26. As will be apparent, these keys engage the ledges defined by the walls of the slot and the abutments defined by the blade head and provide a very strong and positive connection between the blade and the shroud.

The keys 34 are retained against displacement length= wise of the keys by a sheet metal retainer 36 which ex tends through the slot 26 in a clearance space between the tip of the blade head and the base of the slot.26. As will be apparent from Figures 1 and 3, this retainer is slightly V-shaped so that it is a spring fit in the space to prevent the retainer from rattling or shifting, but the retainer is easy to install, as close clearances are unnec essary. Two tabs or heads 38 are provided on each end of the retainer. The tabs, at one end at least, are in the plane of the major portion of the retainer until it has been inserted in the slot 26. These tabs are then bent inwardly as shown in the drawings. The tabs overlie both a portion of the end of the key 34 and a portionoi 3 the .endof the blade head 28 so that neither the retainer. nor the keys can move chordwise of the blade. V

It will be apparent from the foregoing that the shroud easily installed onthe-blades after .they have been mounted in the rotor. If it should become necessaryto replace a blade, the shroudmay be. cleared-from, the blade by removing only the-two segments which attach to it. These maybe easilyremovedflbybendingup the tabs 38, pushing out the retainerand :the keys, and lifting the segments off the blades.

An important advantage of the structure according to the invention isthe positive, rigid andeasily installed connection between the blade and-the shroud. Another important advantage is therigid but lightweightstructure of the shroud" segment which is formed from sheet metal to provide a box'section, as illustrated in Figure 5, which is very rigid for-its weightand thus will resistany substantial bowing due to the effect of centrifugal force. Because the structure is light, it puts aminimum centrifugal load on the blades.

The detailed description of the'preferred embodiment of the invention for the purpose of explaining the principles thereof is not to be considered as limiting or restricting the invention, as many modifications may be made by the exercise of skill in the art without departing from the principles of the invention.

1 claim:

the blade providing ledgesifacing outwardly from the rotor, each blade having a head on the tip thereof extend ing chordwise of the blade,-the head being dimensioned so as to be insertable radially into the slot and defining a shoulder facing inwardly toward the rotor at each face of the blade, and two keys.,slidably mounted in the slots in the tongues extending between and engaging the shoulders. off-the: blade and the ledges .of: the shroud segment tongues.

4. A shrouded" turbomachine-rotor structurev comprising, in combination,a rotor, a ring of blades,,,extending from the rotor, a shroud mounted on the tips of the blades, the shroud comprising a number .of segments 1. A shrouded turbomachine-rotor structure compn'sing, in combination, a rotor, a ring of blades extending from the rotor, a shroud mounted on the tips of the blades, the shroud comprising a number of segments mounted end-to-end to provide ashroud around the tips of the blades, each shroudsegment having two tongues spaced chordwise of theblade at one end and a tongue at the other end extending between the two tongues at the-said'one end of the adjacent shroud segment, the tongues-having an undercut slot extending chordwise of the blade providing ledges facing outwardly from the rotor, each blade having a head on the tip thereof extendring chordwise of the blade, the head being dimensioned so as to be insertable radially into the slot and defining a shoulder facing inwardly toward the rotor at each face of'the blade, and keys insertable by movement lengthwiseof the slot engaging between the shoulders and the ledges retaining the segments on the blades;

2. A shrouded turbomachine rotor structure comprising, in combination, a rotor, a ring of blades extending from the rotor, a shroud mounted on the tips of the blades, the shroud comprising a number of sheet metal box-section segments mounted end-to-end to provide a shroud around the tips of the blades, each shroud segment having two tongues spaced chordwise of the blade at one end and a tongue at the other end extending between the two tongues at the said one end of the adjacent shroud segment, the tongues having an undercut slot extending chordwise of the blade providing ledges mounted end-toend toprovide ashroud around the tips of the blades, each shroud'segrnent having two tongues spaced chordwise of the blade at one end and a tongue at the other end extending between the two tongues at the saidone endzof, theadjacent shroud segment, the tongues havinganundercut slot extending chordwise of the blade providing ledges facing outwardly. from the rotor, each bladehavinga head on the tip thereof extending chordwise. ofitheblade, the head being dimensionedso as. to be insertable radially, into the, slot-and defining a shoulderfacing inwardly toward the rotor at each face of the blade, two keys slidably mounted in the slots inthe tongues; extending between and, engaging the shoulders'of-thesbladeandthe ledges of the shroud segment tonguesnand airetainerextending through the slot and having tabs adapted'tooverlieboth ends of the keys and'the ends-.of the head of-the blade to retain the keys against chordwise displacement;

5. Atshrouded; turbomachinerotor structure comprising, in combination, a ratora; ring; of-bladestextending from the rotor,- a;v shroud mounted on the tips: of. the blades, the shroud comprising a, number of; segments mounted end-toendttotprovidea shroud around the tips of the blades, each shroud segment having two tongues spaced chordwiseof the blade at one; end and a tongue at-the other endlextending between the two tongues at the said one end of the adjacent shroud segment, the tongues having an undercut slot extending chordwise of the blade providing ledges facing'outwardly from the rotor, each, blade havingv ahead on the tip thereof extending chordwise of the blade, the head being dimensioned so asto be insertable; radially into the slot and defining 'ashoulder facing inwardly toward the rotor at each face of the blade, two keys of L-shaped crosssection slidably mounted in the slots in the tongues exfacing outwardly from the rotor, each blade having a blades, the shroud comprising a number of segments mounted end-to-end to provide a shroud around the tips of the blades, each shroud segment having two tongues spaced chordwise of the blade at one end and a tongue at'the-other end extending-between the two tongues at the-said one end of. the adjacent shroud segment, the tongues -having an undercut slot; extending chordwise of tending between and engaging the shoulders of the blade and the ledges of theshroud segment tongues, and a retainer' extending through the slot and having tabs adapted to overlie both endsof the keys and the ends of the head of the bladeto retain the keys against chordwise displacement.

6. A shrouded turbomachine rotor structure comprising, in combination, a rotor, aring of blades extending from the rotor, a shroud mounted on the tips of the blades, the shroud comprising a number of segments mounted end-to-end to provide a shroud around the tips of the blades, each shroud segment having two tongues spaced chordwise of the blade at one end and a tongue at the other end. extending between the two tongues at the said one end of the adjacent shroud segment, the tongues having'an undercut slot extending chordwise of the blade providing ledges facing outwardly from the rotor, each blade having a head on the tip thereof extending chordwise of the blade, the head being dimensioned so as to be insertable radially into the slot and defining ashoulderfacing inwardly toward the ,rotor'at each face of the blade, two keys slidably mounted in the slotsin the tongues engaging theshoulders of the blade andthe ledges ofthe :shroud segment tongues, and a retainer extending through the slot between the head of the blade/and the. base of the slot and having heads adapted; .to overlie.-botb. endsof: the-keys and ;thQ-.

of the head of the blade to retain the keys against chordwise displacement, the retainer portion extending through the slot being non-planar to provide resilient engagement with the head of the blade and the base of the slot.

References Cited in the file of this patent UNITED STATES PATENTS 969,843 Clarke Sept. 13, 1910 6 Baumann July 16, 1929 Allen Dec. 26, 1944 Thomas et a1. June 23, 1953 Johanson Nov. 10, 1953 Abild Aug. 17, 1954- Kent et a1. Dec. 4, 1956 

